Drive arrangement for a washing or dry cleaning machine

ABSTRACT

An eddy-current motor for driving the drum or basket of a washing or dry cleaning machine, has a disc rotor coupled to the drum and a stator having a plurality of rod-shaped electromagnets whose windings are functionally interconnected in groups, each group defining a different number of poles so that the drum may be rotated at different speeds.

United States Patent [191 Burger 1111 3,840,764 51 Oct. 8, 1974 DRIVE ARRANGEMENT FOR A WASI-HNG OR DRY' CLEANING MACHINE Inventor: Manfred Burger, Wolfratshauser Strasse 45 I, 8023 Pullach, Germany Filed: Aug. 22, 1973 Appl. No.: 390,566

[30] Foreign Application Priority Data Aug. 25, 1972 Germany 2241970 May 7, 1973 Germany 2322859 [5 6] References Cited UNITED STATES PATENTS 10/1895 Gorges 310/268 X 6/1922 Murphy 318/243 X 1/1925 Parvin 318/243 X 1,769,652 7/1930 Smith 310/268 X 2,041,875 5/1936 Stoller 310/185 UX 2,573,283 10/1951 Seitz 310/268 X 2,897,387 7/1959 Welter 318/243 X 2,932,752 4/1960 Jones et a1. 310/166 3,194,032 7/1965 VOn Brimer 310/268 UX 3,223,043 12/1965 Shapiro 310/268 X 3,223,867 12/1965 Shapiro 310/268 X 3,333,443 8/1967 Chung et al. 68/23 3,355,914 12/1967 Venema et a1 68/23.7 3,604,222 9/1971 Wutherich et a1. 68/24 Primary ExaminerD. F. Duggan Attorney, Agent, or Firml-Ians Berman [5 7] ABSTRACT An eddy-current motor for driving the drum or basket of a washing or dry cleaning machine, has a disc rotor coupled to the drum and a stator having a plurality of rod-shaped electromagnets whose windings are functionally interconnected in groups, each group defining a different number of poles so that the drum may be rotated at different speeds.

11 Claims, 8 Drawing Figures PATENIEL GET 8 i914 SHEEY 2 OF 5 SHEET 5 OF 5 PATENTED Um 8 4974 DRIVE ARRANGEMENT FOR A WASHING OR DRY CLEANING MACHINE BACKGROUND OF THE INVENTION a. Fieldof the Invention This invention relates to automatic washing and dry cleaning machines. More particularly, this invention relates to an improved eddy-current drive arrangement for such machines.

b. Discussion of the Prior Art Known automatic washing and dry cleaning machines typically include'a rotatably mounted drum or basket in which the clothes to be cleaned are placed during operationof the machine.

Means are provided to rotate the basket during the cleaning and drying cycles and such means may comprise an ac. motor or, as disclosed in U.S. Pat. No. 3,194,032 which issued July 13, 19.65 to .l. W. Von Brimer, an eddy-current linear actuator motor may be used. As disclosed in theVon Brimer patent, the eddycurrent motor comprises a disc-shaped rotor mounted to the. basket for simultaneous rotation therewith. More specifically the rotor comprises an induction disc of non-magnetic, electrically conductive material in intimate contact with a yoke disc of ferromagnetic material. A stator having a plurality of poles each comprising a plurality of electro-magnetic windings, is positioned adjacent the rotor in such a position as to induce eddy-currents in the rotor. The windings are arranged in groups and means are provided to vary the number of poles in each group. Thus, when the groups of windings are supplied with alternating current of differing phases the stator generates pulsating, phase-shifted magnetic fields offset circumferentially relative to the rotor. The superposition of the pulsating magnetic 1 fields results in a rotating, travelling field which causes the rotor to turn, by induction.

The speed at which the rotor rotates depends upon the speed of the travelling magnetic field which, in turn, depends on the number of poles per group of windings about the circumference of the rotor. By varying thenumber of poles in each group of windings the rotation speed of the rotor may be changed. This is particularly important in washing and dry-cleaning machines which require a relatively low speed for washing and a higher speed for spinning and drying.

To provide this speed changing'capability the stator of machines such as disclosed in U.S. Pat. No. 3,194,032 is provided with a plurality of laminations having notches into which the conductors of the winding groups are placed. This technique, well known in the electric'motor industry, permits the rated current to flow in each winding group when the stator is rotating at the rated speed. The rated current is, of course, substantially smaller than the current which flows when the rotor is held stationary.

This property, which is desirable in conventional electric motors, is undesirable in eddy current motors used in washing and dry cleaning machines. Because of the complex, and therefore expensive, shapeof the stator laminations, the stator must be dimensioned sparingly for its current carrying ability.

Further, in order'to add to the flux circulation the conductors of the several groups of windings must be placed in the notches of the laminations in such a manner that conductors placedin the same notch must all conduct current in the same direction. Thus, the circuitry required to establish the several groups of windings becomes exceedingly complex and expensive. This is particularly true if the windings are to be arranged so that the number of poles in each group may be selectively altered.

Conventional machines of this type are driven by an electric motor which is a compact and independently operated unit, typically mounted on a stand and having a rotor shaft journaled therein. In order to reduce the initial cost of such a washing or dry cleaning machine it is customary to select the smallest possible motor which will do the job, because the cost of the motor is a significant factor in the overall machine cost. The load on the motor depends largely on the weight and distribution of the clothes in the basket. Centrifugal forces exerted on the basket cause substantial additional loads on the motor, particularly during acceleration and deceleration thereof. Peak motor loads may thus occur which are several orders of magnitude larger than the rated load. Conventional washing and drycleaning machines are therefore equipped with extensive over-load protection devices.

With eddy current motors, however, because the rated current is substantially smaller than the current which flows with a stationary basket, particularly complicated measures are required to prevent overload of the stator during start-up. Also, it is impossible to provide electromagnetic braking of the drum, for example by interchanging the phases of two groups of windings, and if the speed of rotation of the drum is to be changed a complex control arrangement is needed.

SUMMARY OF THE INVENTION These and other problems are solved by the instant invention whose basic object is to simplify the above described basket drive arrangement and to render the drive insensitive to overloads.

In a first embodiment of the invention this object is attained by making the pole windings rod magnets each comprising an electromagnetic winding wound on a soft iron core. The iron cores have first pole ends positioned proximate the induction disc and second pole ends abuttingly engaging a soft iron yoke. The iron cores which comprise the groups of windings of differing pole numbers are radially spaced at different dis- 7 tances from the axis of rotation of the rotor.

It will be appreciated that not only is it easier to wind a rod magnet than a gapped core magnet but, because of a rod magnets simpler structure, it is more readily overdimensioned than a conventional slotted magnet. The soft iron cores can, therefore, be positioned in front of the rotor with optimum utilization of the given shape of the washerbasket, without concern for any increase in the rated current. The invention thus provides a basket drive which requires little-space and which does not substantially exceed the space required for the basket itself. Further, the rod magnet windings may be safely operated at current levels which approach the stationary rotor current experienced during start up. Thus, the speed control circuiting for the basket is considerably simplified. a

The energizing current may be switched on or off at any rotary speed between zero and rated speed without any special safety precautions for avoiding overloads in the stator windings. Because of the high moment of inertia of the basket, it is sufficient to provide two limiting values of rotary speed and to monitor these speeds, for example, by a tachometer-generator mechanically switching the energizing current on and off when these limiting values are passed. It is thus unnecessary to provide speed control by means of thyristors or the like, which are expensive at the relatively high current levels involved. The basket drive of this invention is, therefore, particularly suited for washing and dry cleaning machines which require rotary speed ranges to be maintained during the washing cycle as well as the spinning cycle. The direction of rotation may be changed, if desired, for example, by interchanging the phases of the two groups of windings to reverse the direction of the rotating travelling field. Because the rated current and the current with a stalled basket are of the same order of magnitude, the basket drive according to the invention may be used to brake the rotating basket. The mechanical brakes heretofore employed with such machines may therefore be omitted. Because the size limitations imposed on eddy-current motors of the type disclosed in US. Pat. No. 3,194,032 are not present in the instant invention, cooling the rotorpresents no special problem.

Although the torque produced by a rod magnet motor according to this invention decreases with decreased spacing of the soft iron cores from the rotor axis, an embodiment has been found advantageous in which, if the number of poles in each group of windings is different, the group having the smallest number of poles is positioned closest to the axis of rotation. However, when it is desired to attain the greatest possible torque for a given size basket drive, for example where a particularly high spinning speed is required, another embodiment of the invention includes a rotor having two induction discs on either side of a common yoke disc. As in the previous embodiment, the pole magnets are rod magnets wound on soft iron cores, and the cores associated with one group of windings comprising a first number of poles are on one side of the rotor while the other group of windings comprising a second number of poles are on the other side of the rotor. The

first pole ends of the cores are positioned proximate their respective induction discs whilethesecond pole ends engage a soft iron yoke. Preferably, the soft'iron cores on both sides of the rotor are equidistant from the axis of rotation.

In another embodiment ofthe invention, the soft iron cores are positioned at equal distances from adjacent cores associated with the same group of windings. Preferably, the cores are also positioned at equal distances from adjacent iron cores associated with groups of windings of equal numbers of poles. This embodiment is distinguished by a greatly improved freedom from vibration of the rotor, particularly when the cores are circumferentially distributed about the rotor.

When the cores are located relatively far from the axis of rotation, it is mechanically advantageous to make the induction disc, yoke disc and/or the soft iron yoke similar in shape and to give them a radial width substantially equal to the radial dimensions of the pole ends of the soft iron cores.

In order to reduce iron losses it is advantageous to make the yoke disc. soft iron yoke and/or the soft iron cores laminar, conventional transformer laminations being suitable. When the yoke disc and/or the soft iron yoke are annular, they may be formed by winding a ribbon of transformer lamination.

The shape of the fundamental magnetic wave may be improved by providing the pole ends of the iron cores which are adjacent the induction disc with pole pieces which reduce the air gap between pole ends of adjacent iron cores, in the direction of the rotor circumference. This expedient improves the torque and such pole pieces have an approximately trapezoidal cross-section parallel to the induction disc. The windings of the rod magnets in a given group may be connected in series or in parallel, but a series connection is preferred.

In a particularly advantageous embodiment of the invention, two rod windings of one group are separated from each other by a rod winding from each of the other groups. In this arrangement all rod windings will contribute to the total flux, and the flux of one winding will not cancel that of another.

In order to prevent sealing problems with respect to any fluid which may be present in the drum, it is preferred to construct the machine in such a manner that the eddy-current rotor is mounted within the machine housing. This is entirely possible with the instant invention because the rotor requires little space and thus, does not significantly increase the volume of the housing. Keeping the housing volume low is important, particularly, in dry cleaning machines, because of the unavoidable loss of solvent vapor which occurs each time the housing is opened, such losses being directly porportional to the housing volume.

Although dry cleaning solvents are corrosive, the electromagnets need not be encapsulated if the magnets are positioned at least partly, outside of the machine housing. When the electromagnets are provided with pole pieces which pass through the housing and form a portion of the housing wall, the pole pieces may be positioned close to the rotor, thereby enhancing the induction effect.

The invention and its mode of operation will now be described with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified, cross-sectional view of an illustrative basket-drive according to the invention, together with other elements of a washing or drycleaning machine;

FIG. 2 is another view of the apparatus shown in FIG. 1 taken in section on line IIII;

FIGS. 3a and 3b are circuit diagrams of groups of motor windings in the basket drive of FIG. 1;

FIG. 4 is a cross-sectional view of another embodiment of the invention;

FIG. 5 is a plan view of a pieces in FIG. 4;

FIG. 6 is a cross-sectional view of an additional embodiment of the invention; and

FIG. 7 is a cross-sectional view of yet another embodiment of the invention, taken through its axis of rotation.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a washing or drycleaning machine 1 having a housing 2 provided with an access door 3 and enclosing a drum or basket 5 for the goods to be washed or drycleaned. The basket is rotatably supported in a bearing 7 and is connected with an eddycurrent rotor disc 11 of the basket drive motor by a horizontal shaft 9, the disc 11 also being rotatably supported by the bearing 7. A stator 13 carrying a plurality portion of the stator pole of magnetic windings is located proximate the rotor 11 in such a position asto induce an electromagnetic field in the rotor.

The stator 13 is equipped with a plurality of rod magnet windings 17 each of which is wound about a soft iron core releasably fastened to a carrier 19 by a non-magnetic bolt, not illustrated, but common to the several illustrated embodiments of the invention. When the rod magnet windings, which are spaced from each other about the circumference of the rotor 11, are supplied with alternating currents offset in phase, the windings l7 produce magnetic fields which are also offset in phase relative to each other, which, when superimposed on each other, produce an angularly travelling field. Because of the eddy current induced in an induction disc 21 associated with the rotor 11, which is positioned in front of the windings 17, rotor 11 will turn.

The magnetic circuit in each core 15 is closed at one end through a soft iron yoke disc 23 in the rotor 11, and at the other end through an'annular, soft iron yoke 25. In the first embodiment, the cores, as well as the soft iron yokes, are comprised of stacked laminations. Advantageously, thesoft iron yokes 25 may be formed from annularly wound strips of transformer lamination material.

' Some of the magnet windings 17 and cores 15 are omitted from FIG. 1 for the sake of clarity, but FIG. 2 gives a complete view of the stator 13 in section along the line-II II in FIG. 1.-

As shown, the stator 13 is comprised of two separate annular portions 27,29. The speed of rotation of the basket during spinning and during washing is determined by the number of poles in the stator portions 27,29 respectively. In the embodiment illustrated in FIG. 2, the first stator portion 27 has four poles, and the second portion 29 has eight poles. While an adequately high spinning speed is generallyreached with four poles on the stator'portion 27, rotary speeds low enough for washing are preferably produced by more than eight poles, the number shown in the drawing being eight for the convenience of pictorial representation only. The cores-l5 and the corresponding core windings 17 on eachstator portion 27,29 are equally spaced from each other and are equally spaced from the axis of rotation. g

FIG. 3a illustrates the series connection of the windings 17 on the eight-pole, second stator portion 29 which are arranged in groups 31. Three groups 31 are provided to supply the second stator portion 29 with three-phase AC. Four windings l7, uniformly distributed about the circumference of the rotor 11, are serially connected in each group 31. Respective windings 17 of the two other groups are circumferentially interposed between each pair of adjacent windings 17 in one group 31, in uniform sequence. The groups 31 have respective terminal connections U,V,W and X,Y,Z by means of which the groups may be connected to a suitable three-phase supply system in either a Y or delta connection. FIG. 3b shows the circuit diagram for the four-pole, first stator portion 27 and is analogous to the circuit shown in FIG. 3a. FIG. 3b differs from FIG. 3a essentially in having only two windings 17 serially connected in each group 33.

FIG. 4 shows another embodiment of the invention, analogous elements being provided with the same reference numbers as in the figures described above, augmented by 100. As shown, the rotor- 111 comprises a circular ring and is connected to the shaft 109 for rotation by a hub 135 whichis made from a minimum of material to avoid imbalance. First and second stator portions 127, and 129 respectively are positioned on either side of the rotor 111, and each has a different number of poles. The magnetic flux generated by the rod windings 117 in the cores 115, and in the annular yokes is closed in a circuit including the annular yoke disc 123. In this embodiment, a pair of induction discs 121 are mounted on either side of the yoke disc 123.

FIG. 5 illustrates another arrangement for the pole ends of the cores 15 which are adjacent to the induction disc 23. The pole ends are equipped with generally trapezoidal-shaped pole pieces 200 to improve the torque produced by the motor. The pole pieces 200 provide an airgap of uniform width a between adjacent soft iron cores 15, the air gap a being greater than the spacing of the polepieces 200 from the induction disc.

FIG. 6 shows another drive according to the invention in a washing or drycleaning machine. The reference numerals of elements analogous to elements in FIG. 1 are augmented by 200. A basket 205 is fastened in overhung relationship on a shaft 209 journaled in a bearing 207 in a wall of the machine housing opposite the access door 203, the shaft 209 being rotatably sealed in the machine housing 202. An induction disc 221 is fastened on a hub 214 so that its two opposite rotor surfaces arefreely accessible. The disc 221 is caused to rotate by releasably mounted electromagnets 218 arranged in front of the disc and drives the basket 205 by means of a speed-changing transmission 238 which connects the hub 214 to the shaft 209. The electromagnets 218 have soft iron cores 215 which are provided with windings 217' and pole pieces 216 on each of the two terminal poles which are opposite a radial face of the disc 221. The windings 217 are supplied with AC having an offset phase relationship. The cores 215 of the windings 217, which may be combined into groups each having a different number of poles, may be circumferentially offset, relativeto one other, in uniform sequence with respect to the disc 221. However, an arrangement including features of the apparatus shown in FIGS. land 2 is also possible in which the second stator portion 29, for example, is positioned in front of the disc 221, in addition to the electromagnets 218. Depending on the number of poles in each group of windings, the transmission 238 may be a speedreducing or speed-increasing transmission. The transmission 238 may be a belt transmission or a gear transmission, or it may be constituted by planetary gearing installed directly in the disc 221.

Elements shown in FIG. 7 corresponding to analogous elements in FIG. 1 are provided with the same reference numerals augmented by 300. FIG. 7 shows a washing or drycleaning machine whose basket or drum 305 is guided and supported in a housing 302 by means of a plurality of guide rollers 308. The rollers permit rotary movement, but axially secure the basket 305. A group of rod-shaped electromagnets 318 is mounted on a wall 340 of the machine housing 302, opposite the access door 303. The magnets pass through the wall 340 and consist of soft iron cores 315 enveloped by windings 317. The ends of the magnets 318 remote from the housing 302 are in contact with a common yoke plate 319 of ferromagnetic material, such as soft iron. The

pole ends of the cores 315 in the housing 302 face an induction disc 321 fastened to a radial wall 346 of the basket 305, a soft iron disc 323 being axially interposed between the disc 321 and the wall 346. The cores 315 jointly with the plate 319 and the disc 323 constitute a closed path for magnetic flux, the flux intersecting the induction disc 321 which may consist of copper, aluminum or any other electrically conductive, nonmagnetic material.

The drive arrangements described above are particularly suitable for washing and drycleaning machines of a size adequate for industrial application although with suitable modifications they may also be used in domestic machines. The first stator portion of such a machine will typically have four poles, and thereby permit a spinning rate of from 300 to 800 RPM when exited by AC current of SOHZ. The second stator portion will typically have 30 poles and thus permit a rotary washing speed of from to- 60 RPM. The necessary energizing current for such machines is of the order of 50 to 300 amps.

As previously discussed, it is possible to make either the induction disc or the yoke disc, or preferably both, annular in shape. The radius of each annulus preferably is the same as the radius of the basket. When the induction and yoke discs are annular, then the stator should also be annular. The radial width of the rotor need be no larger than the radial dimension of the pole-ends of the stator cores.

Also, the rotor need not necessarily be a separate element from the disc or drum. It is perfectly feasible to use a portion of the drum itself as the rotor, either by fabricating the entire drum from some suitable electrically conductive material or by fastening a suitable member directly to the drum. One skilled in the art may make various changes to the elements and layout of parts shown, without departing from the spirit and scope of the invention.

What l claim is:

1. Cleaning apparatus comprising a housing, a drum member mounted in said housing, and drive means for rotating said drum member, the drive means including:

a. an eddy current rotor disc mounted on said housing for rotation about an axis and including an induction disc of electrically conductive, nonmagnetic material, and a yoke disc 'of ferromagnetic material in intimate contact with said induction disc;

b. a multi-pole stator mounted proximate said rotor disc in a position to induce eddy currents in said induction disc,

l. said stator including a plurality of rod-shaped electromagnets and at least one soft-iron yoke, 2. each electromagnet including a soft-iron core and an electromagnetic winding thereabout,

3. said windings being arranged in a plurality of conductively connected groups constituting respective pluralities of poles when said windings are energized,

4. the number of poles constituted by a first one of said groups being different from the number of poles constituted by a second group,

5. each soft-iron core having a first pole end facing said induction disc and a second pole end in abutting engagement with said soft iron yoke,

6. the electromagnets associated with said first group being radially spaced from said axis a first distance, and the electromagnets associated with said second group being radially spaced from said axis a second distance different from said first distance; and

c. connecting means drivingly connecting said rotor disc to said drum member.

2. Apparatus as set forth in claim 1, wherein the number of poles constituted by said first group is smaller than the number of polesconstituted by said second group, and said first distance is smaller than said second distance.

3. Apparatus as set forth in claim 1, wherein said rotor disc and said stator are each annular and have respective radial widths substantially equal to the radial dimension of said first pole ends.

4. Apparatus as set forth in claim 1, wherein said connecting means connect said rotor 'disc to said drum member for simultaneous rotation about said axis.

'5. Apparatus as set forth in claim 1, wherein said pole ends have a cross section in a radial plane or generally traguezoidal shape.

. Cleaning apparatus comprising a housing, a drum member mounted in said housing, and drive means for rotating said drum member, the drive means including:

a. an eddy current rotor disc mounted on said housing for rotation about an axis, said rotor disc including a ferromagnetic yoke disc having two oppositely directed, radial faces, and first and second electrically conducting, non-magnetic induction discs in intimate contact with said faces respectively;

b. first and second multi-pole stators on respective axial sides of said rotor disc, said stators being mounted proximate said first and second induction discs respectively for inducing eddy currents in the associated proximate discs,

1. each stator including a soft iron yoke and a plurality of rod-shaped electromagnets, each electromagnet including a soft-iron core and an electromagnetic winding thereabout,

2. the windings of the electromagnets of each stator being conductively connected in at least one group and constituting a plurality of poles,

3. the number of poles in the group of windings of said first stator being different from the number of poles in the group of windings of said second stator,

4. each of said soft-iron cores having a first pole end facing the associated induction disc and said soft-iron yoke; and

c. connecting means drivingly connecting said rotor disc to said drum member.

7. Apparatus as set forth in claim 6, wherein the softiron core of said first and second stators are radially equidistant from. said axis.

8. Apparatus as set forth in claim 6, wherein said rotor disc and said stators are each annular, having respective radial widths substantially equal to the radial dimension of said first pole ends.

9. Apparatus as set forth in claim 1, wherein the cores associated with the windings of each group are equian ularly spaced about said axis.

10. pparatus as set forth in claim 9, wherein each winding of one grou is separated from each angularly adjacent winding 0 said one group by at least one winding of each of the other groups.

11. Apparatus as set forth in claim 1, wherein said stator further includes a support and fastening means releasably fastening each of said electromagnets to said support. 

1. Cleaning apparatus comprising a housing, a drum member mounted in said housing, and drive means for rotating said drum member, the drive means including: a. an eddy current rotor disc mounted on said housing for rotation about an axis and including an induction disc of electrically conductive, non-magnetic material, and a yoke disc of ferro-magnetic material in intimate contact with said induction disc; b. a multi-pole stator mounted proximate said rotor disc in a position to induce eddy currents in said induction disc,
 1. said stator including a plurality of rod-shaped electromagnets and at least one soft-iron yoke,
 2. each electromagnet including a soft-iron core and an electromagnetic winding thereabout,
 3. said windings being arranged in a plurality of conductively connected groups constituting respective pluralities of poles when said windings are energized,
 4. the number of poles constituted by a first one of said groups being different from the number of poles constituted by a second group,
 5. each soft-iron core having a first pole end facing said induction disc and a second pole end in abutting engagement with said soft iron yoke,
 6. the electromagnets associated with said first group being radially spaced from said axis a first distance, and the electromagnets associated with said second group being radially spaced from said axis a second distance different from said first distance; and c. connecting means drivingly connecting said rotor disc to said drum member.
 2. each electromagnet including a soft-iron core and an electromagnetic winding thereabout,
 2. Apparatus as set forth in claim 1, wherein the number of poles constituted by said first group is smaller than the number of poles constituted by said second group, and said first distance is smaller than said second distance.
 2. the windings of the electromagnets of each stator being conductively connected in at least one group and constituting a plurality of poles,
 3. the number of poles in the group of windings of said first stator being different from the number of poles in the group of windings of said second stator,
 3. Apparatus as set forth in claim 1, wherein said rotor disc and said stator are each annular and have respective radial widths substantially equal to the radial dimension of said first pole ends.
 3. said windings being arranged in a plurality of conductively connected groups constituting respective pluralities of poles when said windings are energized,
 4. the number of poles constituted by a first one of said groups being different from the number of poles constituted by a second group,
 4. Apparatus as set forth in claim 1, wherein said connecting means connect said rotor disc to said drum member for simultaneous rotation about said axis.
 4. each of said soft-iron cores having a first pole end facing the associated induction disc and said soft-iron yoke; and c. connecting means drivingly connecting said rotor disc to said drum member.
 5. Apparatus as set forth in claim 1, wherein said pole ends have a cross section in a radial plane or generally trapezoidal shape.
 5. each soft-iron core having a first pole end facing said induction disc and a second pole end in abutting engagement with said soft iron yoke,
 6. the electromagnets associated with said first group being radially spaced from said axis a first distance, and the electromagnets associated with said second group being radially spaced from said axis a second distance different from said first distance; and c. connecting means drivingly connecting said rotor disc to said drum member.
 6. Cleaning apparatus comprising a housing, a drum member mounted in said housing, and drive means for rotating said drum member, the drive means including: a. an eddy current rotor disc mounted on said housing for rotation about an axis, said rotor disc including a ferromagnetic yoke disc having two oppositely directed, radial faces, and first and second electrically conducting, non-magnetic induction discs in intimate contact with said faces respectively; b. first and second multi-pole stators on respective axial sides of said rotor disc, said stators being mounted proximate said first and second induction discs respectively for inducing eddy currents in the associated proximate discs,
 7. Apparatus as set forth in claim 6, wherein the soft-iron core of said first and second stators are radially equidistant from said axis.
 8. Apparatus as set forth in claim 6, wherein said rotor disc and said stators are each annular, having respective radial widths substantially equal to the radial dimension of said first pole ends.
 9. Apparatus as set forth in claim 1, wherein the cores associated with the windings of each group are equiangularly spaced about said axis.
 10. Apparatus as set forth in claim 9, wherein each winding of one group is separated from each angularly adjaceNt winding of said one group by at least one winding of each of the other groups.
 11. Apparatus as set forth in claim 1, wherein said stator further includes a support and fastening means releasably fastening each of said electromagnets to said support. 